Visualization Study Of The Performance Breakdown In The Two-Phase Performance Of An Electrical Submersible Pump
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Barrios (2007) conducted an experimental work in which was demonstrated that the two-phase stage performance of an electrical submersible pump (ESP) is related to the impeller gas and liquid flow pattern as mentioned by Murakami and Minemura (1974a) for a volute-type centrifugal pump. Barrios (2007) proved that the stage head breakdown is a consequence of the gas pocket formation in the impeller channel as in a volute type pump. However, the gas pocket is described as unstable by Murakami and Minemura (1974a) so a slug-flow-like pattern is observed in the impeller channel at the head breakdown conditions. Barrios (2007) observed that the gas segregates near the back shroud after the gas pocket formation so that it is stable and a gas segregated pattern is observed into the impeller. The discrepancy between both studies may imply that different mechanisms are acting in the gas pocket formation and its stability, which finally affects the stage performance. The objective of this research is to study the gas pocket behavior through the visualization of the flow pattern within an ESP impeller at different operating conditions and fluid properties. Therefore, a series of experimental tests has been conducted utilizing a two-stage prototype at rotational speeds between 600 rpm and 1000 rpm, 2 psig inlet pressure and volumetric gas fraction up to 10 percent. This prototype was built with a transparent acrylic casing to easily observe the flow pattern within the impeller, at the diffuser region and at the impeller inlet region. The gas and liquid flow patterns are observed from videos taken with high speed cameras. Two ports for gas injection have been disposed so the gas can be injected directly to the impeller inlet to get the single stage performance or through the first stage to obtain the multistage performance. A combination of different fluids such as distilled water and air, distilled water and sulfur hexafluoride, and air and a mixture of isopropanol (IPA) and water was utilized in this study. The videos show that the gas pocket is small and located near the front shroud at liquid flow rates higher than stage best efficiency point (BEP). It is formed and dragged out by liquid flowing over the gas pocket as mentioned by Murakami and Minemura (1974a). The gas pocket becomes stable once it has grown through the channel cross section area when the liquid flow rate is reduced down to BEP. At this operating condition, the gas pocket reduces the upper flowing area and forces the liquid to flow in the remaining area between the gas pocket and the trailing channel face. Further reduction of liquid flow rate below the BEP causes the gas pocket to segregate forcing the liquid to flow underneath as Barrios (2007) mentioned. The gas pocket is formed even at zero head, which demonstrates that it is a consequence of bubble coalescence within impeller channel. The critical gas fraction for the gas pocket formation varies as a function of gas density while its stability and formation is a function of the surface tension and bubble size.
Gamboa, Jose; Prado, Mauricio (2010). Visualization Study Of The Performance Breakdown In The Two-Phase Performance Of An Electrical Submersible Pump. Turbomachinery Laboratory, Texas A&M University. Available electronically from